Thermoregulation
Learning Objectives 2/13/08
1. Distinguish between the thermoregulators
classified as endotherms and ectotherms,
homeotherms, heterotherms, and poikilotherms
2. Describe the adaptive advantage(s) of
endothermy
3. Discuss the 4 mechanisms utilized by land
homeotherms to balance their heat budget
4. Discuss the roles of the hypothalamus in
vertebrate temperature regulation
5. Compare and contrast some of the physiological
mechanisms involved in acclimatization to new
temperature ranges
Clarification on terms…
Ectotherm (ecto = “outside”) - An animal that derives body
temperature from an external heat source.
Endotherm (endo = “inside”) - An animal that derives
body temperature from internal heat production.
Note: These terms relate to the source of body
heat, not whether the animals are capable of
regulating body temperature.
Why is body temperature homeostasis important?
What must be true in order for an endotherm to maintain
temperature homeostasis?
Poikilotherm (poikilo =“varied”) - body temperature
approximates the ambient temperature. Not capable of
controlling body temperature as ambient temperature
varies. What is the adaptive advantage here?
Heterotherm (hetero = “different”) - regulates body
temperature when active, but allows body temperature to
fluctuate with the environment when inactive.
Homeotherm (homeo = “same”) - controls body
temperature, keeping it relatively constant as ambient
temperature varies.
These terms relate to whether or not the animal is capable of
controlling body temperature.
Describe the advantage to temperature homeostasis from the
fact that animal bodies are made mostly of water.
Heat Exchange Between an
Animal and its Environment
See Fig. 41.15
Body Temperature Regulation:
Endotherm vs. Ectotherm
•What anatomical &
physiological
characteristics are common
among endotherms?
•What other organ systems
are commonly well
developed in endotherms?
•Are all ectothermic animals
correctly described as
“conformers”? Illustrate your
answer with some examples.
Lizard Behavioral Thermoregulation
Behavioral and physiological
mechanisms in Homeotherms
1. Relocation
2. Thermogenesis
a) Shivering
b) Non-shivering
3. Vasoconstriction/vasodilation
4. Evaporative water loss
Heat Exchange in Appendages
Cross-section:
See Fig. 41.20
Leg of a bird or
mammal
Flipper of a seal or whale
Which mechanism of heat transfer is operating here?
Control of Conductance by
Regional Heterothermy
Cold-climate homeotherms can
allow their appendages to cool to
reduce heat loss.
Countercurrent heat
exchange occurs between
warm out-flowing blood in
a central artery and cold inflowing blood in
surrounding veins.
Integumentary System in
Thermoregulation
Organs of thermoregulation in the skin:
•sweat glands
•arrector pili muscle
•vasodilation/vasoconstriction
What organ serves as the control
center to regulate these organs?
Why are there both cold and hot
thermoreceptors in the body?
Temperature Homeostasis in
Humans
Temperature Acclimatization
• Molecular mechanisms
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See p. 916
Make more enzymes (Why?)
Produce enzyme variants (Explain)
Alter cell membrane components (How?)
Produce cryoprotectants (“freeze tolerance”)
Produce stress-induced proteins
• Behavioral mechanisms
– Torpor
• Hibernation (winter torpor)
• Estivation (summer torpor)
• Diurnal (daily, often nocturnal) torpor
The Fluid Cell Membrane
How does the behavior of the cell membrane change with temperature?
How does the chemical make-up influence this behavior?
Wood frog, Rana sylvatica
(glucose acts as a cryoprotectant)
Wood frog in summer
Wood frog, frozen
The “winter” frog is in cardiac arrest, & has 65% of its body water frozen.
If ECF water freezes, what would happen to ICF water?
Heat-shock proteins protect and
chaperone other proteins
•Produced in response to
various forms of stress: temp,
hypoxia, pH, cancer, etc.
•Protein clumps are seen in the
neurons of patients with Mad
Cow disease and Alzheimer’s
disease.
What cell function may be
faulty in these disease
processes?